September 2013 storms (probably) set new Colorado rainfall record

It’s official – almost. Colorado set a new 24-hour rainfall record when 11.85 inches fell from midnight to midnight on Sept. 12, 2013.

The measurement was taken at a rain gauge maintained by the U.S. Geological Survey at Fort Carson, south of Colorado Springs. It eclipses the previous record of 11.08 inches set in 1965 in Holly.

The Colorado Climate Extremes Committee unanimously approved the new record. It now goes to the National Oceanic and Atmospheric Administration’s National Climatic Data Center for review. The agency must approve it before it enters the official U.S. record books.

“We anticipate it will be approved, but there’s no guarantee,” said Nolan Doesken, the state climatologist based at Colorado State University and chair of the committee. “It won’t appear in the national database until then.”

Committee members include representatives from the National Weather Service offices serving Colorado (Boulder, Grand Junction, Pueblo, and Goodland, Kan.), the NWS Central Region Headquarters in Kansas City, and the University of Nebraska’s High Plains Regional Climate Center.

Before a statewide weather record is declared, several criteria must be met, including:
• The measurement must be taken at a well-functioning gauge maintained by a trained observer/data technician.
• Someone other than the observer must independently evaluate the measurement.
• The observation must be part of a series of observations or network of stations that can establish a climatology for the location and provide context.
• The measurement must be nominated for consideration.
• The observation must be archived indefinitely where the public has unrestricted access to it now and in the future.
• The previous record must be verified.
• Approval by NOAA’s National Climatic Data Center.

The new record was nominated by the National Weather Service office in Pueblo.
“The data showed there was a significant amount of rain in a short period of time,” said Jennifer Stark, the meteorologist in charge at the Pueblo office. “More than two thirds of the precipitation (8.7 inches) recorded that day fell between 6 p.m. and 9 p.m. when a band of heavy rain stalled over the site.”

While 11.85 inches may be the new record, it does not mean it was the most rain that fell in 24 hours in Colorado during September’s severe storms.

“This is the amount that fell in an official gauge and that has been scientifically verified by the committee,” Doesken said.

The most rain ever reported to have fallen in Colorado in a single day was 24 inches near what is now Bonny Reservoir. The May 1935 estimate was based on water measured in a rancher’s new water stock tank so it is not recognized as an official record. (Experts believe it is a reasonable measurement based on the flooding of the Republican River and loss of life.)

“It’s not an official record, but we still use it when we talk about the history of rainfall in Colorado,” Doesken said.